Lubiprostone (1) is an E1 type prostaglandin derivative. It is marketed in USA as Amitiza® and used for the treatment of idiopathic chronic constipation, irritable bowel syndrome and post operative ilues. The use of Lubiprostone softens the stool, increases motility, and promotes spontaneous bowel movements (SBM). Chemically, Lubiprostone is 7-[(2R,4aR,5R,7aR)-2-(1,1-difluoropentyl)-2-hydroxy-6-oxooctahydrocyclopenta[b]pyran-5-yl]heptanoic acid (Drugs of the Future, 2004, 29(4); 336-341):

U.S. Pat. No. 5,117,042 discloses a method of treatment for improving encephalic function which comprises administering, to a subject in need of such treatment, a 15-keto-prostaglandin compound in an amount effective for improvement of encephalic function.
U.S. Pat. No. 5,284,858 teaches the novel 13,14-dihydro-15-keto prostaglandins E and use for treatment and prevention of several types of ulcers, such as duodenal ulcer and gastric ulcer.
U.S. Pat. No. 7,355,064 discloses an improved method for preparing 15-keto prostaglandin E derivative. According to U.S. Pat. No. 7,355,064, the deprotection of protected hydroxyl group required in manufacturing a 15-keto-prostaglandin derivative is conducted in the presence of a phosphoric acid compound.
US 2007244333 discloses a method for preparing a prostaglandin derivative of formula (A):
which comprises reacting an aldehyde represented by formula (B):
with a 2-oxoalkyl phosphonate in a reaction solvent under the presence of alkali hydroxide as sole base. By carrying out the reaction using an alkali hydroxide as sole base in the reaction system, the desired prostaglandin derivative can be obtained by simple procedures and with high yield.
U.S. Pat. No. 5,229,529 provides a method of preparing α,β-unsaturated ketolactones which are useful for production of prostaglandins having one or more halogen substituent(s) at the 16 or 17 position in high yield, in which, a dimethyl(2-oxoalkyl)phosphonate having one or more halogen substituents, a starting material, is reacted with a bicyclolactone aldehyde in the presence of an alkali metal hydride and a zinc compound.
U.S. Pat. No. 5,468,880 describes a method of producing α,β-unsaturated ketones by reacting aldehyde with 2-oxoalkyl phosphonate, wherein the reaction was carried out in the presence of a base and a zinc compound.
U.S. Pat. No. 6,414,016 provides an anti-constipation composition containing a halogenated-bi-cyclic compound as an active ingredient in a ratio of bicyclic/monocyclic structure of at least 1:1.